Digital media production commonly uses source material originating from video cameras, film scanners, animation systems, and diverse sound sources covering dialog, music and natural sound. The data from these sources is called “essence”. Essence enters the production systems as digital data streams and as files, and is stored within systems in solid state memory, on hard disks and data tape. The essence is normally encoded as a series of editable units, called frames, of some tens of milliseconds duration.
Often, picture, sound and other sources are input simultaneously and time-synchronously, and may be stored multiplexed together as a single file, or in separate files. Frames of the essence are often labeled with a timecode number measured in hours minutes seconds and frames; in other cases the sources are labeled by their ordinal number relative to the start of a segment. The production process involves selecting subsections of the input sources and placing them adjacent in intended presentation time and by combining several source signals to produce a new composite signal. As the essence is processed through a system, it is repeatedly stored and replayed from the storage medium. The size of the data files is large, ranging from megabytes to terabytes in size, which is of a size approaching that where the bit error rate of storage media implies a not insignificant number of errors accumulating during a single production. In addition, the repeated editing operations and rearrangement of the input material provides many opportunities for inadvertent introduction of errors.
The reliability of production systems can benefit for a range of error checking and detection systems such as check codes and hash codes, however, until now, these techniques have typically been applied only to complete files which limits their applicability at multiple sequential stages of the production chain.